Evolutionary relationships of a new genus and three new species of Omomyid primates (Willwood Formation, Lower Eocene, Bighorn Basin, Wyoming)

Abstract

Studies of new finds of omomyid primates from the lower Eocene Willwood Formation of northwest Wyoming reveal the presence of a new genus and two new species of anaptomorphines and a new species of omomyine. All were apparently short-lived immigrants into the Bighorn Basin. The new genus and species Tatmanius szalayi is typified by a diminutive single-rooted p3 and a bilobed-rooted p4 with a crown smaller than ml. These traits were probably derived from Pseudotetonius and parallel similar conditions in Trogolemur and Nannopithex. The new species Arapahovius advena is the first occurrence of Arapahovius outside the Washakie Basin, where it appears to have also been a vagrant species. Steinius annectens, sp. nov., is larger than the older Steinius vespertinus and strengthens the alliance between this genus and Bridgerian Omomys carteri, although which species of Steinius is closer to Omomys is not yet clear. The available evidence suggests a derivation of Omomys (Omomyini) from Steinius and all Washakiini from the anaptomorphine Teilhardina, which would indicate that Omomyinae were at least diphyletic. Preliminary evidence suggests that the geographic distributions of at least some Willwood omomyids correlate with paleosol distributions.